19,070 research outputs found
The optimal momentum map
The presence of symmetries in a Hamiltonian system usually implies the
existence of conservation laws that are represented mathematically in terms of
the dynamical preservation of the level sets of a momentum mapping. The
symplectic or Marsden--Weinstein reduction procedure takes advantage of this
and associates to the original system a new Hamiltonian system with fewer
degrees of freedom. However, in a large number of situations, this standard
approach does not work or is not efficient enough, in the sense that it does
not use all the information encoded in the symmetry of the system. In this
work, a new momentum map will be defined that is capable of overcoming most of
the problems encountered in the traditional approach.Comment: 35 pages. To appear in: Geometry, Dynamics, and Mechanics: 60th
Birthday Volume for J.E. Marsden. P. Holmes, P. Newton, and A. Weinstein,
eds., Springer-Verlag, New York, 200
A symplectic slice theorem
We provide a model for an open invariant neighborhood of any orbit in a
symplectic manifold endowed with a canonical proper symmetry. Our results
generalize the constructions of Marle and Guillemin and Sternberg for canonical
symmetries that have an associated momentum map. In these papers the momentum
map played a crucial role in the construction of the tubular model. The present
work shows that in the construction of the tubular model it can be used the so
called Chu map instead, which exists for any canonical action, unlike the
momentum map. Hamilton's equations for any invariant Hamiltonian function take
on a particularly simple form in these tubular variables. As an application we
will find situations, that we will call tubewise Hamiltonian, in which the
existence of a standard momentum map in invariant neighborhoods is guaranteed.Comment: 14 page
The Mexican Animal Identification System: Current Situation, Problems, and Potential
Mexico initiated a federal animal identification (ID) system (SINIIGA) in 2003. The program is administered by an agency of the federal Department of Agriculture (SAGARPA) and has been used primarily to support a federal subsidy program for livestock producers. The program is conceptually well designed, but implementation thus far falls short of the potential and needs, most importantly in animal disease management. Although substantial numbers of animals have been tagged, relatively little progress has been made in developing a usable animal ID information system. Animal health officials currently are not actively involved in the development and use of the system.Mexican animal ID system, livestock, Mexico, Agribusiness, Agricultural and Food Policy, Farm Management, International Development, Livestock Production/Industries, Political Economy, Q13, Q18,
Unveiling the circumstellar environment towards a massive young stellar object
As a continuation of a previous work, in which we found strong evidence of
massive molecular outflows towards a massive star forming site, we present a
new study of this region based on very high angular resolution observations
with the aim of discovering the outflow driven mechanism. Using near-IR data
acquired with Gemini-NIRI at the broad H- and Ks-bands, we study a region of
22" x 22" around the UCHII region G045.47+0.05, a massive star forming site at
the distance of about 8 kpc. To image the source with the highest spatial
resolution possible we employed the adaptative optic system ALTAIR, achieving
an angular resolution of about 0.15". We discovered a cone-like shape nebula
with an opening angle of about 90 degree extending eastwards the IR source
2MASS J19142564+1109283, a very likely MYSO. This morphology suggests a cavity
that was cleared in the circumstellar material and its emission may arise from
scattered continuum light, warm dust, and likely emission lines from
shock-excited gas. The nebula, presenting arc-like features, is connected with
the IR source through a jet-like structure, which is aligned with the blue
shifted CO outflow found in a previous study. The near-IR structure lies ~3"
north of the radio continuum emission, revealing that it is not spatially
coincident with the UCHII region. The observed morphology and structure of the
near-IR nebula strongly suggest the presence of a precessing jet. In this study
we have resolved the circumstellar ambient (in scale of a thousand A.U.) of a
distant MYSO, indeed one of the farthest cases.Comment: Accepted in A&A Letters (October 2013
Energy Shaping Control of an Inverted Flexible Pendulum Fixed to a Cart
Control of compliant mechanical systems is increasingly being researched for
several applications including flexible link robots and ultra-precision
positioning systems. The control problem in these systems is challenging,
especially with gravity coupling and large deformations, because of inherent
underactuation and the combination of lumped and distributed parameters of a
nonlinear system. In this paper we consider an ultra-flexible inverted pendulum
on a cart and propose a new nonlinear energy shaping controller to keep the
pendulum at the upward position with the cart stopped at a desired location.
The design is based on a model, obtained via the constrained Lagrange
formulation, which previously has been validated experimentally. The controller
design consists of a partial feedback linearization step followed by a standard
PID controller acting on two passive outputs. Boundedness of all signals and
(local) asymptotic stability of the desired equilibrium is theoretically
established. Simulations and experimental evidence assess the performance of
the proposed controller.Comment: 11 pages, 7 figures, extended version of the NOLCOS 2016 pape
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